TONUS code

Bibliographie

[Hydrogen explosion simulation and modelling]

TexteZone1

The TONUS code is a single tool for processing all phenomena relating to the risk of hydrogen (distribution, combustion, detonation) likely to occur in a pressurised water reactor containment in a severe accident. TONUS version V2006.1 was delivered in June 2006, thus ending the code's development cycle commenced in 1995, in conjunction with the French Atomic Energy Commission (CEA).

TONUS is used to:

predict gas distribution in the containment and pressure loads generated by hydrogen combustion;

simulate all phenomena relating to hydrogen distribution, deflagration and detonation, taking account of the impact of methods to limit the effects of hydrogen explosion.

Models

TONUS is made up of three modules based on two different approaches:

the multi-compartment approach (Lumped Parameter (LP)), which resolves mass and energy balance equations in control volumes called compartments (which may be fictitious). The quantity movement conservation equation is not resolved, but approached by exchange terms between the compartments. This approach is used for one of the code modules,

the multi-dimensional approach (Computational Fluid Dynamics (CFD)), which involves resolving localy containment thermohydraulic equations (multi-species Navier-Stokes equations) coupled with turbulent models, condensation models, combustion models, etc. Two modules use this approach: the first adopts a low-mach formulation resolved with the finite element method whereas the second is based on a compressible formulation and a numeric finite volume algorithm.

The two approaches are complementary. The lumped parameter approach does not cover all the flow conditions encountered in a reactor. The CFD approach can compensate for this, but requires a far longer calculation time. Coupling the two approaches (0D and 3D modules in the TONUS code) is one way of processing, at reasonable cost, areas expected to show a homogenous concentration or one beyond the flammability limits, using the lumped parameter approach, and areas with a more significant hydrogen risk, using the CFD approach.

Qualification

The TONUS code qualification matrix has been constructed under a PIRT type approach (Phenomena Identification Ranking Table), so that separate effect tests (SETs), coupled effect tests (CETs) and integral tests (Iets) are all available. The SETs and CETs tests have been performed on facilities like TOSQAN (located at Saclay and operated by IRSN) and MISTRA (located at Saclay and operated by CEA) for the distribution, and ENACCEF (installed at CNRS Orléans and co-financed by IRSN) for the combustion. The integral tests took place in full-scale facilities like HDR (Germany), NUPEC (Japan) and RUT (Russia). Some of these tests figuring in the qualification matrix were performed under European projects such as HYCOM or OECD projects like ISP47, ECORA and SETH, where TONUS was able to confirm its ability to predict the distribution and pressure loads generated by hydrogen combustion.

Applications

IRSN has in particular applied the TONUS code to assessing pressure loads generated by hydrogen combustion in the nuclear auxiliary building of a reactor at the Chinon power plant and in the 7TNA2 room on the Creys-Malville site. In 2006, and more recently in 2010, IRSN used the TONUS code to asses the impact of the "two zone" concept on hydrogen distribution and combustion in the EPR reactor containment (European Pressurised Reactor). Under future developments, the TONUS code could simulate the distribution and combustion of explosive gases other than hydrogen which could be released during a laboratory or plant accident involving radioactive materials.